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APPENDIX                                  269

Uramil and potassium cyanate unite to form potassium pseudo-
urate,

NH-CO                             Nil—CO

II                 I     I

CO CIINH.-fOCNK =   CO CH.NH.CO.NHK.

II          II

NH—CO                              NH—CO

Potassium pseudourate.

When free pseudouric acid is heated with 20 per cent, hydro-
chloric acid it yields uric acid,

NH-CO                           NH—CO

II         II

CO     CH.NH.CO.NH2   = CO '   C—NIL

II                       I         ||           >CO + HoO.

NH—CO                            NH—C—NH/

Pseudouric acid.                                   Uric acid.

Other synthetic methods are also known for which a book of
reference must be consulted.

PREPARATION 42.

Caffeine. — The close relationship existing between uric acid
and caffeine has long suggested the possibility of converting uric
acid, a comparatively plentiful material, into caffeine, an important
and costly drug, occurring only in small quantities in tea and
coffee. The problem has been solved by E. Fischer, who has
succeeded in synthesising caffeine in a variety of ways. Fischer
found that by using the same series of processes as described
above in the synthesis of uric acid, but substituting dimethyl-
alloxan for alloxan, and methylamine sulphite for ammonium
sulphite, trimethyl uric acid is formed, and is identical with
hydroxycaffeine,

CH3N -- CO

I         I

CO    C-N(CH3)

I         /C°     "

CH3N - C— NH

Tritnethyl uric acid (Hydroxycaffeine).

Hydroxycaffeine is converted into caffeine by acting upon  i
with a mixture of phosphorus pentachloride and oxychloride.

it                   J
I